Intramolecular Nitrene Insertion Research Articles

Synthesis of α-, β-, and γ-Carbolines via Intramolecular Cyclization of Azidomethyl(indolyl)acrylates Involving PIFA-BF3·OEt2/DBU-Mediated Cyclization as well as Thermolysis Approaches.

In this study, we present our findings on the synthesis of α-, β-, γ-carbolines via PIFA/BF3·OEt2-mediated intramolecular cyclization of isomeric azidomethyl(indolyl)acrylates. Alternately, 1,5,7-triazabicyclo[4.4.0]dec-5-ene/1,8-diazabicyclo(5.4.0)undec-7-ene (TBD/DBU)-mediated Michael addition followed by intramolecular cyclization of isomeric 2/3-(azidomethyl)indol-3/2-yl)acrylates also furnished the respective β- and γ-carboline derivatives. Unexpectedly, the thermolysis of 2-(azidomethyl)-3-(indol-3-yl)acrylates led to the formation of ethyl 5-(2-(phenylsulfonamido)aryl)nicotinates along with γ-carbolines, via nitrene insertion followed by rearrangement and cyclization. The isomeric 2-(azidomethyl)-3-(indol-2-yl)acrylate upon thermolysis led to the expected δ-carboline. Thermal intramolecular nitrene insertion reaction could also be extended for accessing pyrido benzothiophene, pyrido thiophene, and quinoline.

Tailoring C-H amination activity via modification of the triazole-derived carbene ligand.

Two new C,O-bidentate chelating triazolylidene-phenolate ligands were synthesized that feature a diisopropylphenyl (dipp) and an adamantyl (Ad) substituent respectively on the triazole scaffold. Subsequent metalation afforded iron(II) complexes [Fe(C^O)2] that are active catalysts for the intramolecular C-H amination of organic azides. When compared to the parent complex containing a triazolylidene with a mesityl substituent (Mes) the increased steric bulk led to slightly lower activity (TOFmax = 23 h-1vs. 30 h-1), however selectivity towards pyrrolidine formation increases from 92% up to >99%. Kinetic studies indicate that the mechanism is similar in all three complexes and includes a half-order dependence in [Fe(C^O)2], congruent with the involvement of a dimetallic catalyst resting state within this catalyst class. Structural analysis suggests that enhanced bulkiness disfavors N2 loss and nitrene formation, yet shields the nitrene from intermolecular processes and thus favors intramolecular nitrene insertion into the C-H bond. This model rationalizes the high selectivity and the lower reaction rate observed with dipp and with Ad substituents on the ligand.

Intramolecular Nitrene Insertion into Saturated C-H-Bond-Mediated C-N Bond Cleavage of a Coordinated NHC Ligand.

Ruthenium(II) complexes bearing a tridentate bis(N-heterocyclic carbene) ligand reacted with iminoiodanes (PhI=NR) resulting in the formation of isolable ruthenium(III)-amido intermediates, which underwent cleavage of a C-N bond of the tridentate ligand and formation of an N-substituted imine group. The RuIII -amido intermediates have been characterized by 1 H NMR, UV/Vis, ESI-MS, and X-ray crystallography. DFT calculations were performed to provide insight into the reaction mechanism.

Catalyst-Controlled Diastereoselective Synthesis of Cyclic Amines via C-H Functionalization.

Reliable regio- and stereochemical techniques applicable to nonactivated aliphatic systems remain largely elusive due to the challenges of discriminating between multiple, relatively strong sp3 C-H bonds whose chemical behavior often differ only subtly. Nevertheless, approaches that employ directing groups and/or auxiliaries have emerged, but impose practical restrictions, especially in complex molecule synthesis. This report describes a catalyst-controlled regio- and diastereoselective synthesis of N-unprotected pyrrolidines via dirhodium catalyzed intramolecular nitrene insertion into sp3 C-H bonds. The reaction proceeds at rt without external oxidants, nitrene stabilizing groups, or directing functionality. The insights that emerged from the conformational/stereoselectivity relationships (CSR) between catalysts and substrates provide a framework for rational catalyst design that can accommodate a broader range of aliphatic C-H chemistry.

Tuning the strain effect to induce selectivity through intramolecular nitrene insertion into an adjacent methoxy C[sbnd]H bond leading to form a new benzoxazole: experimental and computational studies

Pyrolysis of azido-meta-meconine yields only a single product 1D, which has been characterized spectroscopically (1H NMR, 13C NMR, HSQC, DEPT & MS). These results reveal that the fused five-member lactone ring can influence the product selectivity. The DFT calculations suggest the formation of favourable oxazolidine intermediate compared to azirine (1Z) and ketenimine (1H) intermediates. The isodesmic analysis showed that the fused lactone aryl nitrene (1N) would have more strain to form azirine (1Z) intermediate than the corresponding aryl nitrene (1M).

ChemInform Abstract: Enantiospecific Total Synthesis of N‐Methylwelwitindolinone D Isonitrile.

ChemInform Abstract: Enantiospecific Total Synthesis of N‐Methylwelwitindolinone D Isonitrile.

Concomitant Nitrene and Carbene Insertion Accompanying Ring Expansion: Spectroscopic, X-ray, and Computational Studies

Reinvestigation of the thermolysis of azido-meta-hemipinate (I) yielded, in addition to known II, unusual products III and IV. These products are formed via a rare intramolecular nitrene insertion into an adjacent methoxy C-H bond followed by an intermolecular reaction during a ring-expansion and a ring-extrusion reaction followed by a carbene insertion. The structures of the new compounds were confirmed using a battery of techniques, including HRMS (ESI-QTOF) and 2D NMR as well as X-ray crystallography for compound IV. Density functional theory methods were used to support the proposed mechanism of formation of the products.

RuIV(F20-TPP)Cl2] efficiently catalysed inter- and intra-molecular nitrene insertion into sp3 C–H bonds of hydrocarbons using phosphoryl azides as nitrene sources

[Ru(IV)(F20-TPP)Cl2][H2(F20-TPP) = meso-tetrakis(pentafluorophenyl)porphyrin] is an active catalyst for both inter- and intra-molecular nitrene insertion into sp(3) C-H bonds of hydrocarbons in good to high product yields using phosphoryl azides as nitrene sources.

Total Synthesis of (−)-N-Methylwelwitindolinone C Isothiocyanate

We report the first total synthesis of (-)-N-methylwelwitindolinone C isothiocyanate. Our route features a number of key transformations, including an indolyne cyclization to assemble the [4.3.1]-bicyclic scaffold, as well as a late-stage intramolecular nitrene insertion to functionalize the C11 bridgehead carbon en route to the natural product.

ChemInform Abstract: Intramolecular Nitrene Insertions into Aromatic and Heteroaromatic Rings. Part 9. Synthesis of 2-Azidodiphenylmethanes and the Kinetics of Their Thermal Decomposition in Solution.

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Synthesis of 6-methyl-6 H-indolo[3,2- c]isoquinoline and 6-methyl-6 H-indolo[2,3- c]isoquinoline: two new unnatural isoquinoline isomers of the cryptolepine series

11 H-indolo[3,2- c]isoquinoline has been synthesized in two steps starting from 4-bromoisoquinoline and 2-bromoaniline via a selective Buchwald–Hartwig reaction followed by a Pd-catalyzed intramolecular direct arylation involving C(sp 2)–H activation. The synthesis of 7 H-indolo[2,3- c]isoquinoline was achieved by a combination of a Suzuki reaction with an intramolecular nitrene insertion reaction starting from 4-bromoisoquinoline and {2-[(2,2-dimethylpropanoyl)amino]phenyl}boronic acid. Selective methylation of the tetracyclic skeletons yielded the title compounds 6-methyl-6 H-indolo[3,2- c]isoquinoline and 6-methyl-6 H-indolo[2,3- c]isoquinoline, which have never been described in the literature before.

Synthesis of the Benzo‐β‐Carboline Isoneocryptolepine: The Missing Indoloquinoline Isomer in the Alkaloid Series Cryptolepine, Neocryptolepine and Isocryptolepine.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of the benzo-β-carboline isoneocryptolepine: the missing indoloquinoline isomer in the alkaloid series cryptolepine, neocryptolepine and isocryptolepine

7 H-Indolo[2,3- c]quinoline has been synthesized in two steps via a new approach starting from commercially available 3-bromoquinoline and 2-bromoaniline. The new methodology consists of two consecutive palladium-catalyzed reactions: a selective Buchwald/Hartwig amination followed by an intramolecular Heck-type reaction. Alternatively, the same skeleton has also been prepared via the combination of a Suzuki arylation with an intramolecular nitrene insertion starting from 4-chloroquinoline and {2-[(2,2-dimethylpropanoyl)amino]phenyl}boronic acid. Selective methylation of 7 H-indolo[2,3- c]quinoline yielded 5-methyl-5 H-indolo[2,3- c]quinoline (Isoneocryptolepine) which is an interesting new lead compound in the search for new antiplasmodial drugs.

Total Synthesis of a Novel 2‐Thiabicyclo[3.2.0]heptan‐6‐one Analogue of Penicillin N.

Abstract A route has been developed which allows synthesis of novel cyclobutanone analogues of penicillin. This is illustrated by the synthesis of (1R,4R,5R,5′R,7S)-( 1b ) and (1S,4S,5S,5′R,7R)-7-[5′-amino-5′-carboxy]pentanamido]-2-thiabicyclo[3.2.0]heptan-6-one-4-carboxylate ( 1a ), an analogue of penicillin N. The key steps in the synthesis were the formation of the bicyclic structure via a [2+2] cycloaddition and the introduction of nitrogen at C7 via an intramolecular nitrene insertion.

Total synthesis of a novel 2-thiabicyclo[3.2.0]heptan-6-one analogue of penicillin N

A route has been developed which allows synthesis of novel cyclobutanone analogues of penicillin. This is illustrated by the synthesis of (1 R,4 R,5 R,5′ R,7 S)-( 1b ) and (1 S,4 S,5 S,5′ R,7 R)-7-[5′-amino-5′-carboxy]pentanamido]-2-thiabicyclo[3.2.0]heptan-6-one-4-carboxylate ( 1a ), an analogue of penicillin N. The key steps in the synthesis were the formation of the bicyclic structure via a [2+2] cycloaddition and the introduction of nitrogen at C7 via an intramolecular nitrene insertion.

Synthesis of a novel thiabicyclo[3.2.0]heptan-6-one analogue of penicillin

Synthesis of (1SR, 4SR, 5SR, 7RS)-7-(tert-butoxycarbonylamino)-2-thiabicyclo[3.2.0]heptan-6-one-4-carboxylic acid ethyl ester, a novel cyclobutanone analogue of a β-lactam antibiotic is described. This was achieved by [2+2] cycloaddition of a 2,3-dihydrothiophene with dichloroketene, followed by conversion to a cyclobutanol and use of an intramolecular nitrene insertion strategy to install nitrogen functionality at C-7 with endo stereochemistry.

Photo amidoglycosylation of an allal azidoformate. Synthesis of beta-2-amido allopyranosides.

[figure: see text] Photolysis of an allal C-3 azidoformate provoked intramolecular nitrene insertion into the glycal C=C unit and allowed direct incorporation of alcohol nucleophiles as beta-disposed substituents at C-1. The 2-amido allopyranoside products were elaborated via N-acylation and selective oxazolidinone hydrolysis, providing N-Boc-protected 2-amino sugars and simplifying stereochemical assignments. Synthesis of the potentially labile allal azidoformate was achieved via reaction of the corresponding carbonyl imidazolide with trimethylsilyl azide, facilitated by dibutyltin oxide.

The synthesis of pyrido(2,3,4-kl)acridine unit of some marine alkaloids

A simple and convenient synthesis of pyrido(2,3,4-kl)acridine (1), the main skeleton of some marine alkaloids, via cyclization and intramolecular nitrene insertion, is described. The importance of the planarity of the molecule during the nitrene insertion is explained.Key words: pyridoacridine, marine alkaloids, nitrene insertion, quinoline, quinolinone.

An Efficient Synthesis of [15N]-Carbazole from [15N]-Aniline

A reaction sequence involving ortho-lithiation of [15N]-(tert-Butoxy-carbonyl)aniline, quenching with Bu3SnCl, palladium catalyzed coupling with bromobenzene, and deprotection provides efficient access to [15N]-2-aminobiphenyl (4). Compound 4 is converted to [15N]-carbazole via diazotization, treatment with NaN3, and heating to promote intramolecular nitrene insertion.

Preparation of enantiomerically pure fructose-derived 1,3-oxazin-2-one by INIR methodology and its application as a chiral auxiliary in some model asymmetric reactions

A newly developed fructose-based homochiral 1,3-oxazin-2-one reagent prepared via a regioselective and stereoselective intramolecular nitrene insertion reaction (INIR) exerts smooth stereocontrol resulting in high levels of asymmetric induction and chemical yield in various synthetic transformations including aldol, Diels-Alder cycloaddition and α-bromination reactions.